Advantech UTC-124G3 screen flickering after kernel patch: `drm/i915/dp: Recheck link state after modeset`

On boot, the Advantech UTC-124G3 flickers consistently. This behavior happened as a result of this patch: drm/i915/dp: Recheck link state after modeset.

Steps to reproduce:

• power on the device and the screen will begin to flicker

I am currently running the latest stable 6.6 kernel as the drmtip kernel does not boot on this device.

reven ~ # uname -a
Linux localhost 6.6.63-06119-g336c44901d5e #1 SMP PREEMPT_DYNAMIC Mon, 2 Dec 2024 21:44:56 +0000 x86_64 Intel(R) Celeron(R) CPU J3455 @ 1.50GHz GenuineIntel GNU/Linux
reven ~ # lspci -vnn -d :*:0300
00:02.0 VGA compatible controller [0300]: Intel Corporation HD Graphics 500 [8086:5a85] (rev 0d) (prog-if 00 [VGA controller])
	DeviceName: Onboard - Video
	Subsystem: Intel Corporation Device [8086:2212]
	Flags: bus master, fast devsel, latency 0, IRQ 126
	Memory at 90000000 (64-bit, non-prefetchable) [size=16M]
	Memory at 80000000 (64-bit, prefetchable) [size=256M]
	I/O ports at f000 [size=64]
	Expansion ROM at 000c0000 [virtual] [disabled] [size=128K]
	Capabilities: [40] Vendor Specific Information: Len=0c <?>
	Capabilities: [70] Express Root Complex Integrated Endpoint, IntMsgNum 0
	Capabilities: [ac] MSI: Enable+ Count=1/1 Maskable- 64bit-
	Capabilities: [d0] Power Management version 2
	Capabilities: [100] Process Address Space ID (PASID)
	Capabilities: [200] Address Translation Service (ATS)
	Capabilities: [300] Page Request Interface (PRI)
	Kernel driver in use: i915
	Kernel modules: i915

This is a touchscreen device with no external monitors attached.

Attached are the dmesg logs with drm.debug=0x1e, log_buf_len=4M and ignore_loglevel enabled.

advantech_dmesg_full.txt

added Community feature: display/Other platform: APL labels

I've found that from the aforementioned patch it's the delayed recheck link function that's running in an infinite loop on the device. The constant link checking is what's causing the screen to flicker on and off.

I've proposed a patch here which adds a quirk that will skip over the link checking for this device. With this patch applied the flickering goes away.

I wonder if PSR is supported by the panel and hence

commit facde55b6fca80fc6c8d051e932085bd3e7c6d04
Author: Jouni Högander <jouni.hogander@intel.com>
Date:   Tue Oct 29 14:24:15 2024 +0200

    drm/i915/psr: WA for panels stating bad link status after PSR is enabled

in drm-tip would fix the problem. @jdenose , could you try applying the above commit (still checking here if it needs a non-trivial rebase on 6.6) and provide a dmesg log booting with drm.debug=0x11e log_buf_len=20M containing the boot-up messages as well (up to the issue indicated by the 8b/10b link not ok, retraining message in dmesg)? Alternatively you can also use journalctl -k -o short-monotonic to get dmesg.

Thanks.

• @jhogande

Hi Imre, thank you for your reply.

This commit did not resolve the flickering issue. Attached are the dmesg logs with the command line arguments you specified.

advantech_dmesg_full_psr.txt

Checked advantech_dmesg_full_psr.txt. Based on that I say PSR is not supported by the setup.

@jdenose , could you please:

• Make sure you have CONFIG_DRM_DISPLAY_DP_AUX_CHARDEV=y in your .config
• Apply your patch (so that the link does not get retrained)
• Boot with drm.debug=0xe (so that AUX transfers will not flood the log)
• After the display gets enabled, wait 3 seconds
• Dump the full DPCD, while the display is still enabled correctly, by either:
  • sudo dd if=/dev/drm_dp_aux0 of=dpcd.bin
    or if the above fails:
  • sudo ddrescue /dev/drm_dp_aux0 dpcd.bin

In the end, please attach both dmesg and dpcd.bin + the stdout/stderr output of dd/ddrescue.

Thanks.

Here's the output after doing what you asked for:

# dd if=/dev/drm_dp_aux0 of=dpcd.bin
2048+0 records in
2048+0 records out
1048576 bytes (1.0 MB, 1.0 MiB) copied, 131.89 s, 8.0 kB/s

dpcd.bin dmesg_w_dpcd.txt

@ideak friendly ping! Is there anything else that you need from me?

@jdenose , thanks for the logs. I think the following would be the proper way to work around the monitor's link status reporting issue. Could you try if the issue is resolved applying these on drm-tip?:
0001-drm-Add-DP-quirk-for-non-standard-link-status-report.patch
0002-drm-i915-Work-around-Advantech-CH7511-link-status-re.patch

@ideak yes, those patches together resolve the flickering issue and the screen works as expected!

Okay, thanks for the testing (and also for the report and initial patch). I can follow up with this version shortly.

Hello @ideak should I be looking out for those patches somewhere?

Hi @ideak, I wanted to follow up on these patches which resolve the flickering issue. Are they going to be submitted upstream?

added feature: display/DP feature: display/eDP labels